1. Field of the Invention
This invention relates to the field of acid hydrolysis extrusion technology. In particular, it pertains to a method and apparatus for the acid treatment of cellulosic materials and employs an extrusion apparatus having a pretreatment zone, a reaction zone, a plurality of acid injection ports associated with the reaction zone, and a pressure sensitive, variable die separating the pretreatment and reaction zones. A unique die construction having a frustoconical orifice of specified pitch is provided that virtually eliminates the surging and blowing usually experienced during the extrusion of cellulosic or like fibrous materials.
2. Description of the Prior Art
Extrusion hydrolysis of cellulosic material has been recognized as a possible economical method for hydrolyzing large quantities of cellulose into simple sugars suitable for conversion into liquid fuels by fermentation. The presence of an acid solution within an extruder barrel at elevated pressures and temperatures, however, has in the past presented a problem of rapid deterioration of the component parts of the extruder. Elevated temperatures and pressures are required in cellulose hydrolysis not only to effect the hydrolysis, but to break down the coarse cellulosic material to a texture that is amenable to the controlled hydrolysis of the material. Also, the extrusion of cellulose or like fibrous materials has in the past been accompanied by severe surging and blowing of the material in the extruder barrel, making the extrusion process difficult or impossible to control.
A method and apparatus for the extrusion hydrolysis of cellulosic material that would economically process large quantities of cellulose at elevated temperatures and pressures, eliminate surging and blowing, and minimize the acid deterioration of the component parts of the extruder, would be a decided advantage.